Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.79   10.518%   $64.9735   $64.97   $64.95   $65.00  
  Purchase #2 $154.51   8.294%   $167.3251   $167.33   $167.35   $167.30  
  Purchase #3 $137.32   12.705%   $154.7665   $154.77   $154.75   $154.80  
  Purchase #4 $49.28   6.263%   $52.3664   $52.37   $52.35   $52.40  
  Purchase #5 $244.54   11.582%   $272.8626   $272.86   $272.85   $272.90  
  Purchase #6 $119.42   4.694%   $125.0256   $125.03   $125.05   $125.00  
  Purchase #7 $127.63   4.235%   $133.0351   $133.04   $133.05   $133.00  
  7 purchase totals = $891.49       $970.3548   $970.37   $970.35   $970.40